/Engine/Source/Runtime/JsonUtilities/Public/JsonObjectConverter.h
Optional callback that will be run when exporting a single property to Json. If this returns a valid value it will be inserted into the export chain. If this returns nullptr or is not bound, it will try generic type-specific export behavior before falling back to outputting ExportText as a string.
typedef TBaseDelegate_TwoParams< [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FJsonValue](API\Runtime\Json\Dom\FJsonValue) >, [FProperty](API\Runtime\CoreUObject\UObject\FProperty) *, const void * > CustomExportCallback